1. Field of the Invention
This application is an improvement over U.S. Pat. No. 5,351,986 issued to William E. Hedenberg et al. which relates to air suspension systems applicable to and useful for vehicles, particularly for pickup trucks, recreational vehicles (RVS) and vans. U.S. Pat. No. 5,351,986 is incorporated herein by reference.
2. Description of the Related Art
A present trend in the development of load carrying vehicles is to provide a vehicle with an empty weight as low as possible and a load carrying capacity as large as possible. In an empty state the damping is often too high (too hard) and in the loaded state the damping is often too low (too soft). The inventor has found that an answer to this problem of load dampening sensitivity is the use of an air suspension system wherein the axle frequency of vibration of about 1.16 to 1.25 Hz remains unchanged throughout the entire load range.
Another patent of interest to the present invention is U.S. Pat. No. 5,697,635 issued to Koster et al. which discloses a pneumatic suspension assembly for vehicles wherein an air suspension system and the shock absorbers are supplied by the same air supply and are electronically controlled. The shock absorbers are also electronically controlled independently of the air spring to provide damping during critical driving conditions. The present invention provides a simplified system wherein the air springs and the damping forces of the shock absorbers automatically adjust to the varied load conditions. The shock absorbers are initially selected or tuned for vehicles of different load ranges.
This invention relates to an improved air suspension system for the rear axle of a vehicle such as a pickup truck wherein an air spring is mounted directly on a lever arm and the air spring and lever arm support the weight of the vehicle frame and load. In one embodiment, the lever arm has its forward end supported on a roller bushing of a bracket assembly mounted on the axle housing. The bushing provides a rolling and shifting action for the lever arm. The rear end of the lever arm is affixed to a frame bracket mounted on the vehicle chassis. The system further employs adjustable hydraulic shock absorbers pneumatically controlled by the same source of compressed air that supplies the air spring.